1. Field of the Invention
The present invention relates to an air conditioner, and more particularly, to a system and method for controlling a temperature of a refrigerant in an air conditioner, in which a supper-heating degree and/or a supper-cooling degree can be secured by controlling an amount of refrigerant which is heat exchanged due to a difference in temperature of refrigerant at a predetermined position of a pipe connecting an indoor unit and an outdoor unit.
2. Description of the Related Art
An air conditioner is an apparatus that can control air temperature, humidity, stream and cleanliness so as to make comfortable circumference. Recently, a multi-type air conditioner has been developed. The multi-type air conditioner includes a plurality of indoor units installed in partitioned spaces and controls air temperatures of the respective spaces.
A heat pump system can be used both as a cooling system and a heating system in accordance with a refrigeration cycle and a heating cycle. The refrigeration cycle makes a refrigerant flow through a normal passage and the heating cycle makes a refrigerant flow through a reverse passage.
FIG. 1 illustrates a relationship of a general refrigeration cycle and a Molier diagram. As shown in FIG. 1, the refrigeration cycle is performed by iterative operations of refrigerant compression, condensation, expansion and vaporization.
A compressor 10 compresses an introduced refrigerant and discharges a high-temperature and high-pressure heated vapor to an indoor heat exchanger 15. At this point, a state of the refrigerant discharged from the compressor 10 becomes a superheating degree (SH), which exceeds a saturated state on the Molier diagram.
An outdoor heat exchanger 15 performs a heat exchange between the discharged high-temperature and high-pressure refrigerant with an outdoor air, resulting in a phase change into a liquid state. At this point, heat of the refrigerant is removed by air passing through the outdoor heat exchanger 15, such that its temperature is rapidly lowered. As a result, the refrigerant is transferred in a liquid state of a supercooling degree (SC).
An expander 20 decompresses the suppercooled refrigerant, making it easy to evaporate the refrigerant at the indoor heat exchanger 25.
The indoor heat exchanger 25 performs a heat exchange between the decompressed refrigerant with the outdoor air. At this point, heat of the refrigerant is removed by air passing through the indoor heat exchanger, such that its temperature increases. As a result, phase of the refrigerant is changed into a liquid state.
The refrigerant introduced from the indoor heat exchanger 25 to the compressor 10 becomes a gaseous state of a superheating degree TSH, in which it is evaporated over the saturated state.
In the relationship between the refrigeration cycle and the Molier diagram, the refrigerant passes through the compressor 10, the outdoor heat exchanger 15, the expander 20, and the indoor heat exchanger 25. The refrigerant discharged from the indoor heat exchanger 25 is again introduced into the compressor 10.
While the refrigerant is transferred from the indoor heat exchanger 25 to the compressor 10, the phase of the refrigerant is changed into the superheating degree. That is, the refrigerant introduced into or discharged from the compressor 10 must be a complete liquid state.
However, it is a theoretical result and a predetermined error occurs in an actual application to the products. Also, when an amount of refrigerant flowing during the refrigeration cycle is relatively small or large compared with the heat exchange state, the phase change does not occur completely in the respective processes.
Due to these problems, the refrigerant introduced from the indoor heat exchanger 25 to the compressor 10 is not changed into a complete superheated vapor and it often exists in a liquid state. When the refrigerant of a liquid state is accumulated in an accumulator (not shown) and introduced into the compressor 10, a noise occurs increasingly and performance of the compressor is degraded.
Also, when the heat pump system changes from the heating mode to the defrosting mode or from the defrosting mode to the heating mode, a probability that the refrigerant of a liquid state will be introduced into the compressor 10 is very high. The reason for this is that the refrigerant flow is changed while the heat exchanger acting as the indoor heat exchanger operates as a condenser during the mode switching process and, on the contrary, the heat exchanger acting as the outdoor heat exchanger operates as an evaporator.
The refrigerant introduced into the compressor 10 is made to have the superheating degree (TSH) by controlling a flow rate of the refrigerant using the expander 20, thereby preventing a phenomenon that the refrigerant of a liquid state is excessively accumulated in the accumulator and then introduced into the compressor. Here, the expander 20 includes a linear electronic expansion valve (LEV) or an electronic expansion valve (EEV). This valve will be referred to as an EEV.
The multi-type air conditioner includes at least one outdoor unit and a plurality of indoor units connected to the outdoor unit, and it operates in a heating mode and a cooling mode. Such a multi-type air conditioner tends to be developed to selectively operate in a heating or cooling mode with respect to the individual rooms.
The related art air conditioner has following problems.
As a supercooling degree for the inlet flow of the indoor unit is degraded according to installation conditions of short/medium/long pipes and height differences, a refrigerant flow noise occurs severely due to the expander included in the indoor unit.
In the related art air conditioner, a current state of the refrigerant is measured using a sensor or the like, which is installed in the inlet and outlet pipes of the outdoor heat exchanger or the compressor. Then, a supercooling degree and a superheating degree are calculated and controlled using the current state of the refrigerant. In this case, however, there occurs a problem in that the supercooling degree cannot be secured due to a pressure loss under the installation conditions of the long pipe and height difference.
Also, the supercooling degree may be degraded because the multi-type air conditioner has a bad branching characteristic or a length of the pipe after a branched pipe is long.
Further, when a refrigerant noise claim occurs in the multi-type air conditioner, an algorithm for the outdoor unit or a structural design must be modified.
Like this, it may be difficult to secure the supercooling degree due to the pressure loss or heat loss, which occurs under the installation conditions of the long pipe and height difference. In this case, a refrigerant noise may occur very seriously.